Thermal treatment apparatus, semiconductor device fabrication apparatus, load-lock chamber

ABSTRACT

A semiconductor device fabrication apparatus includes a thermal treatment device for thermally processing a semiconductor substrate, a first oxygen monitor for monitoring the density of oxygen in said thermal treatment device, a load-lock chamber separably coupled to said thermal treatment device for housing the semiconductor substrate before thermal treatment thereof by said thermal treatment device, and a second oxygen monitor for monitoring the density of oxygen in said load-lock chamber. First, the semiconductor substrate is introduced into the load-lock chamber, and then the load-lock chamber is evacuated. Thereafter, the density of oxygen in the load-lock chamber is measured by the second oxygen monitor, and the thermal treatment device is evacuated, after which the density of oxygen in the thermal treatment device is measured by the first oxygen monitor. The semiconductor substrate is introduced from the load-lock chamber into the thermal treatment device after the densities of oxygen in the load-lock chamber and the thermal treatment device as measured by the first and second oxygen monitors, respectively, have dropped below a predetermined level. A thin film is deposited on the semiconductor substrate in the thermal treatment device.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a thermal treatment apparatus, asemiconductor device fabrication apparatus, a load-lock chamber of sucha semiconductor device fabrication apparatus, and a method offabricating a semiconductor device using such a thermal treatmentapparatus or such a semiconductor device fabrication apparatus.

2. Description of the Prior Art

Recently, it has been of an important task in semiconductor fabricationtechnology to suppress the formation of a native oxide film. If a nativeoxide film is formed on a semiconductor substrate, then the leakagecurrent of a semiconductor device that is fabricated is increased, thedielectric strength thereof is lowered, and the operating speed thereofis adversely affected.

Various efforts have been made to suppress the formation of a nativeoxide film. For example, there has been developed a load-locksemiconductor device fabrication apparatus for suppressing the formationof a native oxide film which would otherwise be deposited on the surfaceof a semiconductor substrate by oxygen trapped in a reaction chamber ina vertical low-pressure chemical vapor deposition (LPCVD) system. Theload-lock semiconductor device fabrication apparatus has a load-lockchamber disposed between the reaction chamber and the exterior space forholding the inlet of the reaction chamber out of contact with theatmosphere. After the load-lock chamber is evacuated, an N₂ atmosphereis introduced into the load-lock chamber. Quantitative data have beenacquired which indicate the relationship between the densities of oxygenin the load-lock chamber and the reaction chamber and the thickness of anative oxide film. The effectiveness of the load-lock chamber is beingwidely recognized in the art.

In CVD systems, it is known that a trace amount of oxygen leaks from theexterior into a semiconductor device fabrication apparatus, e.g., fromthe exterior through an O-ring of a reaction chamber of quartz into thereaction chamber. The oxygen leakage causes a native oxide film to beformed on a semiconductor substrate, and also degrades thecharacteristics of a thin film deposited on the semiconductor substrate.Examples of degraded characteristics include many grain boundaries in acrystalline thin film and wrong crystalline directions.

It is important that semiconductor device fabrication apparatus beprovided with load-lock chambers for mass-producing semiconductordevices fabricate semiconductor devices of stable and reproduciblecharacteristics. However, there have not been proposed any significantmeans and systems for ensuring suring oxygen densities in load-lock andreaction chambers for stable and reproducible semiconductor devicecharacteristics. Furthermore, no measures are presently taken to preventa trace amount of oxygen from leaking into semiconductor devicefabrication apparatus.

It is known to monitor a moisture in sputtering apparatus. Japaneselaid-open patent publication No. 3-152924, for example, discloses amonitoring process for photo-excited vapor phase processing. However, ithas not been known to monitor the density of oxygen in semiconductordevice fabrication apparatus or the like.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a thermaltreatment device capable of eliminating adverse effects which wouldotherwise be caused by residual oxygen.

Another object of the present invention is to provide a semiconductordevice fabrication apparatus and a load-lock chamber which prevent anative oxide film from being formed on a semiconductor substrate therebyto fabricate a semiconductor device whose characteristics are notdegraded by oxygen.

Still another object of the present invention is to provide a method offabricating a semiconductor device using such a thermal treatment deviceor such a semiconductor device fabrication apparatus.

According to an aspect of the present invention, there is provided anapparatus for thermally treating a semiconductor conductor substrate,comprising a thermal treatment device for thermally processing asemiconductor substrate, and an oxygen monitor for monitoring thedensity of oxygen in the thermal treatment device.

According to another aspect of the present invention, there is provideda load-lock assembly for holding a semiconductor substrate beforethermal treatment thereof, comprising a load-lock chamber for housing asemiconductor substrate therein, and an oxygen monitor for monitoringthe density of oxygen in the load-lock chamber.

According to still another aspect of the present invention, there isprovided an apparatus for fabricating a semiconductor device, comprisinga thermal treatment device for thermally processing a semiconductorsubstrate, a first oxygen monitor for monitoring the density of oxygenin the thermal treatment device, a load-lock chamber separably coupledto the thermal treatment device for housing the semiconductor substratebefore thermal treatment thereof by the thermal treatment device, and asecond oxygen monitor for monitoring the density of oxygen in theload-lock chamber.

The thermal treatment device may comprise a chemical vapor depositiondevice.

Each of the oxygen monitors may comprise a mass spectrum analyzer.

According to yet another aspect of the present invention, there isprovided a method of depositing a thin film on a semiconductor substratewith a semiconductor device fabrication apparatus having a thermaltreatment device associated with an oxygen monitor, the methodcomprising the steps of evacuating the thermal treatment device,thereafter, measuring the density of oxygen in the thermal treatmentdevice with the oxygen monitor, introducing a semiconductor substrateinto the thermal treatment device after the density of oxygen in thethermal treatment device as measured by the oxygen monitor has droppedbelow a predetermined level, and depositing a thin film on thesemiconductor substrate in the thermal treatment device.

According to yet still another aspect of the present invention, there isprovided a method of depositing a thin film on a semiconductor substratewith a semiconductor device fabrication apparatus having a thermaltreatment device associated with a first oxygen monitor, and a load-lockchamber associated with a second oxygen monitor, the load-lock chamberseparably communicating with the thermal treatment device, the methodcomprising the steps of introducing a semiconductor substrate into theload-lock chamber, then, evacuating the load-lock chamber, thereafter,measuring the density of oxygen in the load-lock chamber with the secondoxygen monitor, evacuating the thermal treatment device, thereafter,measuring the density of oxygen in the thermal treatment device with thefirst oxygen monitor, introducing the semiconductor substrate from theload-lock chamber into the thermal treatment device after the densitiesof oxygen in the load-lock chamber and the thermal treatment device asmeasured by the first and second oxygen monitors, respectively, havedropped below a predetermined level, and depositing a thin film on thesemiconductor substrate in the thermal treatment device.

Since the thermal treatment device and/or the load-lock chamber isassociated with the oxygen monitor, the oxygen density in the thermaltreatment device and/or the load-lock chamber can be monitoredaccurately at all times. If the monitored oxygen density in the thermaltreatment device and/or the load-lock chamber is higher than thepredetermined level, then the process of fabricating semiconductordevices can immediately be interrupted.

The above and other objects, features, and advantages of the presentinvention will become apparent from the following description when takenin conjunction with the accompanying drawings which illustrate preferredembodiments of the present invention by way of example.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a vertical cross-sectional view of a semiconductor devicefabrication apparatus according to the present invention which iscomposed of a vertical LPCVD device (thermal treatment device) and aload-lock chamber.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As shown in FIG. 1, a semiconductor device fabrication apparatusaccording to the present invention comprises a thermal treatment devicein the form of a vertical LPCVD device and a load-lock chamber, and alsohas mass spectrum analyzers as oxygen density monitors.

The vertical LPCVD device comprises a vertical reaction chamber 6surrounded by a heater 7 for heating the reaction chamber 6. A gassupply system for supplying an N₂ gas and a reactive gas is connected tothe reaction chamber 6.

The load-lock chamber, denoted at 5, houses a transfer unit 3 and awafer boat 12 that are vertically movable by an elevator 4. The waferboat 12 serves to carry semiconductor wafers. A furnace inlet cap 13 isattached to a lower portion of the wafer boat 12. The load-lock chamber5 can be filled with an N₂ gas introduced through N₂ gas pipes extendinginto the load-lock chamber 5. The reaction chamber 6 and the load-lockchamber 5 can communicate with each other through a gate valve 8positioned above the wafer boat 12.

A cassette chamber 1 for housing wafer cassettes 9 is disposed outsideof the load-lock chamber 5, and can communicate with the load-lockchamber 5 through a gate valve 25 positioned laterally of the transferunit 3. Each of the wafer cassettes 9 serves to hold semiconductorwafers. The cassette chamber 1 can be evacuated by a cassette chamberpump 10 connected thereto. A gate valve 2 is mounted on an outer side ofthe cassette chamber 1.

The reaction chamber 6 can be evacuated by a pump 24 through an exhaustpipe having valves 18, 22. The load-lock chamber 5 can also be evacuatedby the pump 24 through an exhaust pipe having valves 21, 23.

According to the present invention, a bypass pipe is connected to theexhaust pipe extending from the reaction chamber 6 in bypassingrelationship to the valve 18. An oxygen monitor 14 in the form of a massspectrum analyzer for monitoring the density of oxygen in the reactionchamber 6 is attached to the bypass pipe. Another bypass pipe isconnected to the exhaust pipe extending from the load-load chamber 5 inbypassing relationship to the valve 21. An oxygen monitor 15 in the formof a mass spectrum analyzer for monitoring the density of oxygen in theload-lock chamber 5 is attached to the bypass pipe. Detectors (notshown) are electrically connected to detect output signals produced bythe respective oxygen monitors 14, 15.

A process of depositing a thin film on a semiconductor substrate withthe semiconductor device fabrication apparatus of the above structurewill be described below.

First, semiconductor substrates, i.e., semiconductor wafers, areintroduced into the load-lock chamber 5, and then the load-lock chamber5 is evacuated by the pump 24. Thereafter, the density of oxygenremaining in the load-lock chamber 5 is measured by the oxygen monitor15.

More specifically, after the wafer cassettes 9 carrying semiconductorwafers 11 have been introduced into the cassette chamber 1, the cassettechamber 1 is evacuated by the cassette chamber pump 10 to preventambient air from entering the load-lock chamber 5. At this time, theload-lock chamber 5 has been evacuated by the pump 24 to the same vacuumas the cassette chamber 1. Then, the gate valve 25 is opened, and thewafers 11 are transferred from the wafer cassettes 9 to the wafer boat12 in the load-lock chamber 5 by the transfer unit 3. After the wafers11 are transferred, the gate valve 25 is closed.

Thereafter, while introducing an N₂ gas into the load-lock chamber 5,the load-lock chamber 5 is evacuated by the pump 24 through the valves21, 23 until the load-lock chamber 5 is filled with the N₂ gas. Afterelapse of a certain period of time, the valve 21 is closed, and thevalves 19, 20 are opened to allow the oxygen monitor 15 to monitor theatmosphere in the load-lock chamber 5.

Concurrent with the above operation, the thermal treatment device isevacuated, and then the density of oxygen remaining in the thermaltreatment device is monitored by the oxygen monitor 14.

More specifically, with the gate valve 8 closed, an N₂ gas is introducedinto the reaction chamber 6, and the reaction chamber 6 issimultaneously evacuated by the pump 24 through the valves 18, 22. Afterelapse of a certain period of time, the valve 18 is closed, and thevalves 16, 17 are opened to allow the oxygen monitor 14 to monitor theatmosphere in the reaction chamber 6.

After the oxygen densities in the load-lock chamber 5 and the thermaltreatment device, i.e., the reaction chamber 6, have been reduced belowa predetermined level, the wafers 11 are carried from the load-lockchamber 5 into the reaction chamber 6 for depositing thin films on thewafers 11.

More specifically, if an oxygen density in excess of the predeterminedlevel is detected in the load-lock chamber 5, then the operation of theLPCVD device is interrupted, and the wafers 11 are returned from thewafer boat 12 to the wafer cassettes 9 by the transfer unit 3.

Similarly, if an oxygen density in excess of the predetermined level isdetected in the reaction chamber 6, then the operation of the LPCVDdevice is also interrupted, and the wafers 11 are returned from thewafer boat 12 to the wafer cassettes 9 by the transfer unit 3.

On the other hand, if the oxygen densities in the load-lock chamber 5and the reaction chamber 6 are found normal by the oxygen monitors 15,14, i.e., after the oxygen densities in the load-lock chamber 5 and thethermal treatment device have dropped below the predetermined level, thegate valve 8 is opened, and the wafers 11 on the wafer boat 12 areintroduced into the reaction chamber 6 by the elevator 4. Thereafter, ausual film growth sequence of the LPCVD device is started to depositthin films on the wafers 11 by way of CVD. During the film growth, theinlet of the reaction chamber 6 is closed by the furnace inlet cap 13.

The vertical reaction chamber 6 of the LPCVD device may be replaced witha horizontal reaction chamber of a single-wafer reaction chamber. Thethermal treatment device may be a thermal diffusion device including anannealing furnace or a sputtering device, rather than the CVD device.Preferably, these devices should be arranged in the same manner as shownin FIG. 1.

In the fabrication of semiconductor devices, not all the operation ofthe various illustrated components may be carried out. For example, thevalves 16, 17, 19, 20 may be manual valves, and the oxygen monitors 14,15 may be detachable, with the oxygen densities in the load-lock chamber5 and the reaction chamber 6 being periodically monitored.

The oxygen monitor 15 in the form of a mass spectrum analyzer may bereplaced with an oxygen density detector which is located in theload-lock chamber 4 for monitoring the oxygen density therein at alltimes.

Oxygen may exist in the form of O₂, NOx, COx, or H₂ O. Therefore, eachof the oxygen monitors 14, 15 may be of any type insofar as it candetect oxygen in any of such forms. For example, each of the oxygenmonitors 14, 15 may comprise a mass spectrum analyzer, an oxygen densitydetector of the galvanic cell type, the constant-potential electrolytictype, or the diaphragm electrode type, a solid electrolytic gas sensor,a semiconductor gas sensor, or any of various humidity sensors. However,the mass spectrum analyzer is preferable to the other oxygen monitors.

With the present invention, the oxygen density in the thermal treatmentdevice and/or the load-lock chamber 5 is monitored by the oxygenmonitor. If the monitored oxygen density is in excess of a predeterminedlevel, then it is possible to prevent semiconductor substrates or wafersfrom being introduced into the thermal treatment device. As a result,defective semiconductor devices are prevented from being produced by thethermal treatment device. The thermal treatment device with theload-lock chamber, i.e., a CVD device, can therefore be used tomass-produce semiconductor devices of stable characteristics.

Although certain preferred embodiments of the present invention has beenshown and described in detail, it should be understood that variouschanges and modifications may be made therein without departing from thescope of the appended claims.

What is claimed is:
 1. An apparatus for thermally treating asemiconductor substrates comprising, a cassette chamber into which saidsemiconductor substrate can be placed, a load-lock chamber incommunication with said cassette chamber by a first gate valve, firsttransfer means for moving semiconductor substrates from said cassettechamber into said load-lock chamber, a reaction chamber in communicationwith said load-lock chamber by a second gate valve, an exhaust pump incommunication with said load-lock chamber, means for supplying nitrogengas to said load-lock chamber, first means for measuring oxygen in saidload-lock chamber, and second means for measuring oxygen in to saidreaction chamber.
 2. An apparatus for thermally treating and monitoringsemiconductor substrate according to claim 1 wherein said exhaust pumpis connected to said load-lock chamber by a first conduit and said firstmeans for measuring oxygen connected to said first conduit.
 3. Anapparatus according to claim 1, wherein said thermal treatment devicecomprises a chemical vapor deposition device.
 4. An apparatus accordingto claim 1, wherein said oxygen monitor comprises a mass spectrumanalyzer.